Ankle fractures involving the syndesmosis complex generally have a worse prognosis than comparable fractures without tibiofibular ligament injuries. In 347 examined patients, Egol et al. were able to demonstrate that after 12 months the functional outcome and the pain level were significantly worse in the group with syndesmosis injuries . Chissel et al. already reported poor clinical results in 1995 when syndesmosis width after surgical treatment exceeded the radiologically measured value of > 1.5 mm . Andersen noted a difference of more than 2 mm of the sagitall anterior tibiofibular distance as a predictor for poorer clinical outcome . Moreover, Leeds and Ehrlich proved a significant correlation between arthrosis development and accompanying syndesmosis injury . Current medium-term study results obtained by Veen et al. confirm a significantly higher arthrosis rate associated with ankle fractures with syndesmosis injury . In addition, Ovaska et al. were able to show that, at 59%, misrepositioned syndesmosis is the most frequent cause of revision surgery of ankle fractures .
The intraoperative malposition rate of the distal tibiofibular syndesmosis in closed reduction is up to 52% and can be reduced to 15% by open reduction of the fibula with direct visualisation of the syndesmosis region [3, 18]. However, also malposition rates after open reduction are still high and require a reliable position control of the distal syndesmosis region. All conventional X-ray parameters (tibiofibular clear space, tibiofibular overlap, etc.) do not allow a sufficient assessment of the fibula position to the tibia [5, 19].
This applies to all syndesmosis injuries since Franke et al. could not identify risk factors such as injury type or fracture morphology after analysing 251 patients with syndesmosis injuries, which are associated with a lower rate of syndesmosis malposition .
Relevant evaluation criteria are the position of the fibula in the tibial incisura and the rotation of the fibula considering correct length reconstruction . Measurements 10 mm above the tibial plafond taking into consideration the diastasis and anterior-posterior translation of the fibula were found to be parameters with high interobserver and intraobserver reliability with the position of the foot having no influence on the measurements .
Intraoperative control of the syndesmosis region is possible using 3D image intensifiers. A small case series of 10 patients with syndesmosis injuries was presented by Ruan et al. in 2011 . An intraoperative 3D scan was performed before positioning the adjusting screw with the joint being temporarily adjusted by means of reduction forceps. The measurement parameter was the distance to the anterior and posterior facets of the tibia. The aim was to achieve equal measuring distances. Once fine correction and adjusting screw application had been completed, a final second 3D scan was performed. In all cases, this scan showed a central and symmetrical positioning of the fibula in the tibial incisura.
Moon et al. reported an intraoperative revision rate of 23% using a 3D image intensifier for ankle fractures with syndesmosis injuries .
Franke et al. performed intraoperative 3D scans in 251 consecutive patients with syndesmosis injuries after adjusting screw placement, which resulted in direct intraoperative correction of osteosynthesis in 32.7% of patients . The main reason was a malposition of the fibula in the tibial incisura in 25.5% and a necessary correction of the fracture reduction in 5.2% of the patients. Corrections due to implant misalignments were necessary in 2% of patients.
Davidovitch et al. compared the conventional versus 3D scan controlled intraoperative reduction of the ankle fork in 36 patients. In the relevant measuring range of 2 mm difference, significantly more postoperative malpositions in the control CT were found in the conventionally radiologically controlled group . Our own data showed a lower malpositioning and correction rate of 7% which may be explained by the generally direct visualization of the syndesmosis stabilisation. Another surgical parameter that significantly influences the reduction result is the positioning of the reduction forceps in the anterior third of the tibia .
Compared to CT examinations, intraoperative radiation exposure resulting from the 3D scan can be classified as very low in total. Beerekamp et al. reported a maximum dose of 17 µSV for a 3D extremities scan compared to a 200 µSV dose for a postoperative CT examination .